Radar sensors are used for detecting the traffic surroundings within the scope of driver assistance systems, for example, for radar-assisted distance control (ACC; adaptive cruise control). Such a driver assistance system is discussed, for example, in the publication “Adaptive Fahrgeschwindigkeitsregelung [Adaptive Cruise Control] ACC”, Robert Bosch GmbH, Gelbe Reihe, 2002 edition, technical instruction. In addition to the distance and the relative velocity, the angle of the located objects is also an important measured variable of the radar sensor. In this case, both the horizontal angle (azimuth angle) and the vertical angle (elevation angle) are significant. The azimuth angle is used for estimating the lateral offset and therefore for lane assignment. The elevation angle enables, for example, a differentiation between objects which may be driven under or driven over, and objects which represent real obstructions. Thus, in particular in safety applications (PSS; predictive safety systems), erroneous triggering due to metallic objects such as manhole covers, tin cans, and the like may be avoided.
The azimuth angle resolution capability is usually achieved in that multiple angle-offset radar lobes are generated, in which the radar echoes are analyzed in separate channels. Scanning radar systems are also known, in which the radar lobe is pivoted. The pivoting of the transmitting and/or receiving lobe may be achieved, for example, with the aid of phased-array antennas. The directional characteristic of the antenna array results by superimposing the radiation diagrams of the individual antenna elements.
A radar sensor for motor vehicles is discussed in WO 2012 089 385 A1, using which the elevation angle of located objects may be at least roughly estimated. This radar sensor includes at least one group antenna, which is formed by a linear array of antenna elements, a feed unit for feeding transmission signals having an adjustable phase relationship into the antenna elements, a control unit for controlling the feed unit, and an evaluation device for evaluating received radar echoes and for angle-resolving locating of objects.